Improvement in thread-tension for sewing-machines



E. L.. PRATT. I Tension Device for Sewing Machines. No; 26,537. PatentedDec. 20. 1859.

fiyz UNITED STATES PATENT OFFICE.

E. L. PRATT, OF PHILADELPHIA, PENNSYLVANIA.

Specification forming part of Letters Patent No. 26,537, dated December20,1859.

To to whom, it may concern:

Be it known that I, E. L. PRATT, of the city of Philadelphia, in theState of Pennsylvania, have invented a new and Improved Tension Devicefor Sewing-Machines; and I do hereby declare that the following is afull, clear, and exact description of the construction and operation ofthe same, reference beinghad to the annexed drawings, making a part ofthis specification, in which- Figure 1 is a side elevation, and Fig. 2 atop view, of the same, like letters in the different figures indicatingthe same parts.

In the drawings, A represents the base upon which the said tensiondevice is supported and by which it is attached to the usual needlebaror other suitable part of the machine B and B", the spring-coils; G, theadjusting thumb-screw; D and D, the intervening trans? verse stripsbetween the coils, and E the spool from which the thread E is drawn.

The base A, I make so that it can be conveniently secured to the usualneedle-bar, or to a yielding take-up, or other suitable part ofasewing-machine. It has a projection, Z, in which two slots, f and g, arecut obliquely. In the upper one, f, of these slots one end of theelastic strip which constitutes the coils B and B is fixed in contactwith another part of the same, so as to produce a circle, B, while theopposite end of the strip is carried around, over, and in contact withthe said circle B through the lower slot, and fastened to the block h,which is made to fit against the one side of the projection Z,substantially as shown in Fig. 1. A' small hole is made obliquelythrough this block h, and in this hole the thumbscrew 0 is adapted torotate and bear against the said projection l in such a manner that whenit is screwed forward, its end bearing against the said projection Z,the coil B will be drawn tightly around the inner coil, B. Twoovally-shaped perforations or holes, iand k, are made through the outercoil, B, and near these perforations the strips D and D are in sertedtransversely between the outer and inner coils. so as to separate andleave a clear space between only at and near the said perforations z andk, and so that the thread E can be readily passed through theperforation 1' out between the coils B and B, and thence into the spacebetween the said coils, near D, through cause the two to bear upon asufficient length n of the thread along between the perforations i and kto effect the tension required, and in inserting or changing the threadit is. only necessary to first pass it through the holes and k, and thenbetween the coils B B by pulli'ng the thread, as before described, areadjustment of the coils not being required for the purpose, nor forsubstituting and using a thread of a different size or number.

The friction produced upon the thread by this device can be increased ordiminished to the most minute degree of accuracy by simply rotating thethumb-screw O, and the friction on the thread E in passing between thecoils B and B is necessarily perfectly smooth and uniform, while theyielding of the two coils together upon the base A, during the pull ofthe thread E in sewing, effectually guards against the threads beingbroken by the suddenly changing action of the needle-lever; and

the peculiar elasticcharacter of the said springcoils, arranged togetheras described, makes their frictional or tensile action upon the threadperfectly compensating in relation to any variation of the thickness ornumbers in the different threads, and so dispenses with the necessity ofany readjustment of the said coils B and B for the purpose.

The device described is simple in its construction, not liable, toderangement from use,

and, being light, is especially applicable to take-up as well as to theneedle-bar, or any other suitable part of a sewing-machine for thepurpose. I

I am aware that a tension device consisting of a spring-pressure pad orflat spring made to press the thread against a solid substance has beenused to produce friction. Therefore I do not claim, broadly, the use ofspring-pressure for producing the required friction on the thread insewing-machines; but,

Having fully described the construction and without causing friction onthe openings, and for the better adjusting or changing the thread whilethe spring remains at the proper working tension, as described,

E. L. PRATT.

Witnesses:

BENJ. MoRRIsoN, R. B. KITT.

